1. Field of the Invention
The present invention relates to a plated copper alloy material as an electrically conductive material for connecting parts such as terminals, connectors and junction blocks, which are used for automobiles and consumer electric appliances.
2. Description of the Related Art
Connection of automotive wires is accomplished with tin-plated terminals of copper alloy. A pair of terminals (male and female) of engaging type constitute a connector. An assembly of such connectors is called a multipole connector.
The recent widespread use of electrical equipment in automobiles requires a single connector to have more terminals (or poles) than before. A connector with many poles needs a large physical force for insertion or even needs a special tool for insertion. This lowers the efficiency of assembling work. For this reason, there has been a demand for connectors which can be inserted with smaller forces than before even though the number of poles increases.
Tin-plated terminals permit insertion with smaller forces as the thickness of tin coating decreases. However, this advantage is lost when they are used for automobiles, in which most connectors have been removed from the cabin to the engine room in order to save the cabin space. The ambient temperature in the engine room reaches about 150xc2x0 C. At such a high temperature, the thin tin-plating layer permits copper to diffuse from the copper parent material or (alloying element to diffuse from the copper-alloy parent material) or permits nickel to diffuse from the underlying plating layer, to form an oxide on the surface of the tin-plating layer. This oxide increases the contact resistance of the terminals. The increased contact resistance makes electronic controllers to malfunction. In practice, therefore, it is difficult to reduce the thickness of the tin-plating layer while keeping electrical reliability.
Moreover, the tin-plating layer is subject to corrosion when automobiles are run or parked for a long time in industrial areas where air pollution with sulfur dioxide gas is prevailing. This corrosion reaches the copper alloy parent material, thereby impairing the reliability of the connecting terminals of engaging type.
A copper alloy material with a tin plating layer is used also as a conductive material in a junction block for an automobile. In implementation of electronics parts in the junction block, the material is required to undergo heat treatment at about 100xc2x0 C. and further effect of heat by solder reflowing. Such conditions of heat do not exist in a conventional production process. Accordingly, the circumstances require a copper alloy material with a tin plating layer which maintains solder wettability after undergoing such heat effects. Furthermore, since the junction block is recently installed in an engine room instead of in a cabin in order to save space, the same problems as mentioned above arise.
A lead frame material with improved heat resistance is disclosed in Japanese Patent Laid-open No. 196349/1994. It consists of a parent material of nickel silver and a multi-layered coating film formed thereon by plating from nickel, copper-tin intermetallic compound, and tin. It was found that when the multi-layered coating film is formed on a copper alloy parent material according to the disclosure, the resulting terminals for engaging type need a large force for insertion, easily crack when bent sharply, or increase in contact resistance after reflowing.
In order to improve solder wettability, it is effective to make the thickness of a tin plating layer more than 2 xcexcm which is thicker than that of a conventional material. However, electric reliability (a low contact resistance) can not be maintained after solder reflowing or after a long use in a high temperature only by controlling the thickness of a tin plating layer. Further, generation of pits in a tin plating layer can not be suppressed after reflowing process for producing a tin plated material.
The present invention was completed in view of the foregoing. It is an object of the present invention to provide an electrically conductive material for connecting parts which consists of a parent material of copper or copper alloy and a multi-layered coating film formed thereon by plating from nickel, copper-tin alloy, and tin, which does not crack even when bent sharply, keeps a low contact resistance after standing at high temperatures, has good corrosion resistance to sulfur dioxide gas, and shows good electrical reliability. The material for multi-pole connecting terminals of engaging type should provide also small insertion force. The material for connecting parts of non-engaging type such as a junction block should maintain solder wettability and prevent generation of pits, even after a heat treatment such as reflow soldering.
The present inventors tackled the problem involved in the copper or copper alloy material with plated surface layers which is used for electrically connecting parts.
The present invention is directed to a plated copper alloy material comprising a parent material of copper or copper alloy, a nickel layer formed on said parent material by plating which has a thickness of 0.1-1.0 xcexcm and a copper-tin alloy layer which has a thickness of 0.1-1.0 xcexcm formed on the nickel layer.
In the plated copper alloy, the copper-tin alloy layer contains preferably 35-75 at %, more preferably 45-65 at % of copper.
The plated copper alloy material may additionally have a tin layer having a thickness of less than or equal to 0.5 xcexcm on said copper-tin alloy layer, wherein the tin layer preferably contains 0.001-0.1 mass % of carbon. This material is especially suitable for an engaging type terminal.
The plated copper alloy material may additionally have a tin layer having a thickness of 0.5-2 xcexcm on said copper-tin alloy layer. This material is especially suitable for a non-engaging type terminal.
A process for producing the plated copper alloy material may comprise coating a parent material of copper or copper alloy with a surface coating layer composed of a nickel layer of 0.1-1.0 xcexcm thick, a copper layer of 0.1-0.3 xcexcm thick, and a tin layer of 0.4-0.8 xcexcm thick, wherein the surface coating layer is formed by plating sequentially in the order mentioned and performing heat treatment, thereby forming a copper-tin alloy layer, so that the surface coating layer is composed of the nickel layer, a copper-tin alloy layer, and a tin layer which remains on the copper-tin alloy layer.
In the process, the ratio of the thickness of said copper layer in the surface coating layer to the thickness of the tin layer in the surface coating layer is preferably 0.15-0.68.
In the process, the heat treatment is preferably reflowing which is carried out at 230-600xc2x0 C. for 3-30 seconds.
In the process, the nickel layer can be formed by electroplating with a current density of 3-20 A/dm2, and the copper layer can be formed by electroplating with a current density of 2.5-10 A/dm2 in a plating bath of copper sulfate at 30-40xc2x0 C.
The material according to the present invention keeps good electric reliability (due to low contact resistance) in a high-temperature atmosphere, has good workability for sharp bending without cracking, and has good corrosion resistance to sulfur dioxide gas. Therefore, they keep good electric reliability when used at high temperatures as in the engine room. Connecting terminals of engaging type made of the material according to the present invention permit insertion with a small force and are useful for automotive multi-pole connectors because of easy male-female fitting and of efficient assembling. Connectors of non-engaging type made of the material according to the present invention maintain solder wettability even when a heat treatment is provided in an implementation process.